1. Field of the Invention
The present invention relates to output variable charging circuits and chargers using the same, and more specifically, the invention relates to output variable charging circuits incorporated in portable devices using secondary batteries as power supplies, and chargers using the same.
2. Description of the Related Art
FIG. 3 shows a circuit diagram of a conventional output variable charging circuit and a charger using the same.
In FIG. 3, an output variable charging circuit 1 has a charging control circuit 2, electrolytic capacitors 3 and 4, a current detection resistor 5, a charging current detection circuit 6, a charging voltage detection circuit 7, a selector switch 8, and a charging condition memory circuit 9. The input of the charging control circuit 2 is connected to an external DC power supply 11. In addition, the output of the charging control circuit 2 is connected to an external secondary battery 12. Between the positive poles and negative poles of the input and the output of the charging control circuit 2 are connected an electrolytic capacitor 3 and an electrolytic capacitor 4, respectively. Between the positive pole of the output of the charging control circuit 2 and the secondary battery 12, the current detection resistor 5 is connected in series. In addition, both ends of the current detection resistor 5 are connected to the charging current detection circuit 6, and a side of the current detection resistor 5, where the secondary battery 12 is disposed, is connected to the charging voltage detection circuit 7. The output of the charging current detection circuit 6 and the output of the charging voltage detection circuit 7 are connected to the charging control circuit 2. Furthermore, the selector switch 8 is connected to the charging control circuit 2 via the charging condition memory circuit 9. In this case, the charging current detection circuit 6 and the charging voltage detection circuit 7 together form a charging characteristic detection circuit 10.
Furthermore, a charger 13 is formed by the output variable charging circuit 1 and the DC power supply 11.
In the output variable charging circuit 1 and the charger 13 having such structures, the charging condition memory circuit 9 stores a plurality of charging conditions corresponding to various kinds of secondary batteries such as a lithium-ion battery, a nickel-hydrogen battery, and a nickel-cadmium battery, and circuits connected in series and parallel to the secondary battery. In this case, the charging conditions are referred to as determined values of a charging current and a charging voltage. One of the charging conditions is selected from the charging condition memory circuit 9 by using the selector switch 8 and is input to the charging control circuit 2.
Meanwhile, the charging current detection circuit 6 detects a charging current from voltages of both ends of the current detection resistor 5 and gives a feedback as a charging current detection value to the charging control circuit 2. The charging voltage detection circuit 7 detects a charging voltage and gives a feedback as a charging voltage detection value to the charging control circuit 2. Such an actual charging current and an actual charging voltage represent charging characteristics. In addition, the charging current detection value and the charging voltage detection value obtained by detecting the charging characteristics by the charging characteristic detection circuit 10 are referred to as charging characteristic values. The charging control circuit 2 controls outputs in such a manner that the charging current detection value and the charging voltage detection value fed back from the charging current detection circuit 6 and the charging voltage detection circuit 7 can satisfy a charging condition input in advance from the charging condition memory circuit 9.
In this way, the output variable charging circuit 1 can be used as a charging circuit which can be adapted to a plurality of secondary batteries or the combination thereof, whose charging conditions differ from each other, by using the selector switch.
Meanwhile, when the output variable charging circuit 1 is manufactured as a product to be used by a user, it is necessary to store in advance the kind of a secondary battery required for the user and charging conditions for circuits connected in series and parallel to the secondary battery in the charging condition memory circuit 9. In this case, depending on the kinds of the charging conditions, the memory capacity of the charging condition memory circuit 9 or the number of times of switching performed by using the selector switch 8 is increased. As a result, this causes a problem in that the size and price of the output variable charging circuit 1 increase. In addition, since the output variable charging circuit 1 cannot adapt to charging conditions different from those stored in advance, for example, a new type of secondary battery, or a new combination of conventional secondary batteries, in this case, it is necessary to produce another output variable charging circuit adaptable to those by changing the contents stored in the charging condition memory circuit 9 and the like.